Heat is the tranny killer. If you don't overheat the tranny, then it will probably last at least 100,000 miles before it needs an overhaul.
If your Lariat is like mine, then you have a tranny temp gauge built into the instrument cluster as one of your instrument options. Choose the "gauges" option, then get that tranny temp gauge front and center. Watch it like a hawk when towing, especially on grades or when moving at less than about 50 MPH.
"Normal" is any tranny temp up to around 210°. "Pay Attention" is any tranny temp between 210° and 225°. If it goes over 225°, it's time to slow down a tad, then find a good place to pull over and stop. DO NOT KILL THE ENGINE
. Put the tranny in park or neutral, then elevate the idle RPM to around 1,300 RPM. Continue watching the tranny temp gauge, and sit there twiddling your thumbs until the tranny temp falls below about 220°. Yes, it's boring, but that will give you some incentive to increase tranny cooling capacity.
If your Lariat doesn't have the factory digital tranny temp gauge, then you need to install an aftermarket tranny temp gauge. You don't need digital, but if analog then it must have clear markings so you distinguish tranny temps of 220°, 225° and 230°. 220° is fine, but watch it closely. 225° is the red line. 230° is too hot. Install the gauge sensor (sender) in the pan (sump) so it will be covered with ATF. Or some trannies have a port on the side of the tranny that will give you sump temp. DO NOT
install the sender in a tranny cooler line. Worst case is you must remove the pan, drill a hole in the lower side of the pan, then install a threaded bung in the pan.
Here's the tranny temp gauge I had for over 10 years in my PowerStroke.
List price is about $155 plus the mount, and that price online is about $104 plus the mount. That gauge will work in an F-150, but the install instructions on that website are for diesels only.
If you ever get tranny sump temp up to 225° or more, then you need more tranny cooling capacity. The simplest method is to replace the factory oil-to-air (OTA) tranny cooler with a bigger heat exchanger, but without reducing the flow of ATF through the coolers. If your F-150 doesn't have an OTA tranny cooler, then install the biggest one that will fit in front of the radiator.